Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$7.28	8.572%	$7.904	$7.90	$7.90	$7.90
Purchase #2	$73.63	13.600%	$83.6437	$83.64	$83.65	$83.60
Purchase #3	$110.67	6.751%	$118.1413	$118.14	$118.15	$118.10
Purchase #4	$149.93	4.598%	$156.8238	$156.82	$156.80	$156.80
Purchase #5	$67.82	5.627%	$71.6362	$71.64	$71.65	$71.60
Purchase #6	$50.31	10.306%	$55.4949	$55.49	$55.50	$55.50
Purchase #7	$144.71	13.256%	$163.8928	$163.89	$163.90	$163.90
7 purchase totals =	$604.35		$657.5367	$657.52	$657.55	$657.40